The invention relates to an apparatus for the manufacture of metal powder by atomization from a nozzle with gas, having a spraying tower, a gas recycling system and a gas cleaning apparatus.
Usually, metal powder production apparatus operating on the gas atomization principle are operated without a gas recycling system. The essential reason for this is the idea that cleaning vaporous and/or gaseous impurities as well as entrained particles of metal powder from the circulating gas is difficult to perform and involves high first costs. Since metal spraying is used especially for the production of superalloys for aircraft engine parts, and any chemical or mechanical impurity in the gas results in appreciable impairment of the quality of these parts, gas recycling has, as a rule, been avoided, and the higher gas costs are accepted in the production of the powder.
In a previously proposed apparatus for metal powder manufacture by gas atomization with a gas recycling system, it is known to remove mechanical impurities from the gas leaving the atomizing tower in a number of filters, then to carry it in a partial flow through a scrubber, and return the gas, thus freed of gaseous impurities, to the atomizing tower under elevated pressure. It is a disadvantage of the previously known apparatus that, after each opening of the gas circuit, especially each opening of the atomizing tower itself (e.g., after each batch), it takes a relatively long time before the gas being circulated for scrubbing regains the purity that is necessary for the start of the next batch. It would be conceivable to shorten the start-up time by operating the gas cleaning system, not on partial flow but on full flow. This, however, would require a substantial enlargement of the already complex gas cleaning system and thus result in a further increase of the invested cost.
It is an object of the present invention to improve a system of the kind described above so that shorter start-up time will be achieved without increasing the expense and complexity involved in the gas cleaning.